When an organism is living, the proportion of radiocarbon that it contains compared with the total carbon is in equilibrium with that of the atmosphere. When the organism dies, exchanges with the atmosphere stop and the radiocarbon contents decay according to an exponential law without renewal with the atmosphere. The residual content of radiocarbon in the organism gives the date of its death.
Dating of organic materials up to 45 000 years: wood, coal, bones, ivory, textiles, shells, etc.
Quartz and feldspar crystals contained in a clay accumulate over time the natural radioactivity effects. Upon heating of a clay object, the energy stored by electron traps on these crystals is released as luminescence, resetting the counter. After the heating, the newly emptied electron traps accumulate energy again. The dating consists to heat quartz and feldspar crystals coming from the terracotta to measure the extracted luminescence. This luminescence is proportional to the accumulated energy since the last heating and so to the time elapsed. Depending of the context, either a test or a dating can be performed.
Test of antiquity or dating of terracotta (ceramics, porcelain, etc.) and of casting nucleus. div>
During the refining of lead ore, radioactive elements (uranium and thorium) are removed in the slags. The radioactive “210Pb” in the metal is not renewed by the decay of the uranium and thorium. Then the 210Pb decays according to a decay curve with a half-life of approximately 22 years. The lead 210 detection is indirectly performed by the activity measurement of the polonium 210 with alpha spectrometry. If no activity is detected, it means that the object is older than 110 years.
Gold ore always contains traces of uranium and thorium. When these radioactive elements disintegrate (following a known decay curves), they transmit a helium nucleus. During the melting of gold, the helium escapes from the crystalline structure (degassing) and the uranium and thorium stay, resetting the counter. The amount of helium produced and trapped in the gold after the cast is therefore proportional to the amount of uranium and thorium in gold and to the time since the casting. This technique allows to obtain a date of the manufacturing of the object.